In microbiological screening, reliance is often placed upon the fact that numerous organisms produce certain effective substances such as antibiotics, amino acids, enzymes, vitamins, toxins, etc., which react in a known manner with test microorganisms thereby identifying in a positive manner the microorganism producing the effective substance. For example, a test microorganism known to react in an identifiable manner with an antibiotic produced by a microorganism is contacted with the effective substance produced by the microorganism and the presence or absence of the identifiable reaction is detected thus identifying the microorganism.
Various apparatuses and methods have been suggested in the past for accomplishing such screening procedures. One approach involves the coating of a plate with the microorganisms suspected of producing the effective substance in the form of a colony and overcoating the unknown colony with a second layer of culture medium containing the test microorganism. The test microorganism is one whose growth is inhibited by the antibiotic effective substance produced by the unknown microorganism. If the growth of the test microorganism is inhibited by the antibiotic suspected of being produced by the unknown microorganism, the existence of the latter is positively established. If no inhibition of growth occurs, the absence of the unknown microorganism is unequivocally established.
This apparatus and procedure, however, suffer from several disadvantages. Thus, there is a "smear effect" when applying the second layer of the test microorganism to the colony to be identified. The smear effect renders it difficult to isolate the areas of inhibition of growth after application of the second layer. The smear effect also results in a further distribution of spores or conidiae of the microorganisms to be tested on the plate which grow into additional colonies. A clear and definite assignment of any inhibited areas in the test microorganism to the original colony is then rendered extremely difficult. If there are several microorganisms in the first coating layer, a smearing of the layer by the overcoat of culture medium containing the test microorganism will render it impossible to ascertain which microorganisms cause the inhibited growth areas in the test layer.
It is an object of the present invention to provide a simple efficient method for the screening and identification of microorganisms.